package NetWork;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    //创建socket对象
    private DatagramSocket socket = null;
    //创建构造方法确认端口号并抛出异常
    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    public void start() throws IOException {
        System.out.println("服务器启动!");
        while(true){
            //1.读取请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096] , 4096);
            socket.receive(requestPacket);
            //为了方便在Java 代码中处理二进制数据  (尤其是在后面进行打印) 可以将上面的数据报中的二进制数据,拿出来,构造成String
            String request = new String(requestPacket.getData(),0, requestPacket.getLength());//获取二进制的字节数
            //2.根据请求计算响应
            String response = this.process(request); //这里的this实际上指向的是子类UdpDict的实例
            //3.把响应写回到客户端
                //将响应response的字节数组的大小传递到DatagramPacket中,重新发送回客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),0,response.getBytes().length, //获取字符数
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);

            //打印日志             -> 分别获取请求地址,响应地址,请求,响应
            System.out.printf("[%s:%d] req = %s, resp = %s\n" ,requestPacket.getAddress(),requestPacket.getPort(),
                    request , response);
        }
    }

    //由于当前写的是 "回显服务器"
    public String process(String request){
        return request;
    }
    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);//创建端口号9090
        server.start();//启动服务器
    }
}
